1) Field of the Invention
This invention relates in general to a slow vent valve capable of supplying controlled flow of gas in two stages and, in particular, to such a valve which is suitable for purging or recovering atmospheric pressure in an evacuated vacuum chamber in semiconductor manufacturing equipment.
2) Description of the Prior Art
A variety of valve systems have been developed for a vent of vacuum chambers in semiconductor wafer manufacturing machinery in which the flow of nitrogen gas has to be controlled to return the evacuated vacuum chamber to atmospheric pressure after chemical vapor deposition or sputtering has been performed on a silicon wafer in the chamber.
During the time when it is vented, the vacuum chamber should be maintained in sufficient stillness in order to protect the wafer from being polluted by internally trapped particulate or from being flicked off, the inflow of nitrogen gas into the chamber has to be gentle enough not to raise particulate deposited on the chamber bed or cause an excessive, movement of air.
However, the inflow of gas to the vacuum chamber has to be strong enough to insure effective chamber purging. In addition, if the gas flow is too much throttled, restoring the vacuum chamber to normal pressure will take a much longer time, delaying the entire wafer production time.
The venting valve system illustrated in FIG. 2 may be typically used with a vacuum chamber 1 for wafer manufacturing equipment, which comprises an inlet piping 2, a needle valve 3 and a first air valve 4 provided in series to supply nitrogen gas to recover atmospheric pressure in the evacuated chamber. Also, a second air valve 5 is provided in parallel with the needle valve 3 and the first air valve 4 to supply gas to purge the chamber 1. In addition, connected to the chamber 1 at the downstream side is an exhaust piping 7 which leads to a vacuum pump 8 through a check valve 6, provided to evacuate the vacuum chamber 1.
With this arrangement, when the evacuated vacuum chamber 1 is returned to atmospheric pressure, the first air valve 4 is actuated to open and introduce nitrogen gas into the chamber for a pressure of 200-300 torrs. The needle valve 3 is also operated to control a flow rate so that the entering gas will not blow dust or flip the wafer off its position in the chamber.
In the next step, the second air valve 5 is actuated to fully open; therefore, all the valves 3, 4 and 5 are actuated to open and introduce full flow of nitrogen gas into the chamber.
When any remaining gas within the chamber 1 and connected upper system are to be purged, all the valves are opened to flow into the chamber 1 through the inlet piping 2, with the vacuum pump 8 being put into purge operation of remaining gas to the exhaust pipe 7.
However, those conventional valve systems as the one illustrated in FIG. 2 have been found to pose various problems. For one, they are complicated requiring as many as three valves in a single apparatus. Their design also makes operations cumbersome and brings about maintenance problems, since needle valves normally defy easy servicing access.
Thus, there has been demand for an effective vent system which is simple in construction and effective in venting a vacuum chamber without causing negative effects on wafers in the chamber. It is these drawbacks of the prior art that gave rise to the present invention.